Measurements and/or estimates of exhaust pressure of an exhaust flow flowing through an exhaust passage of an internal combustion engine may be used as inputs in various vehicle control strategies in order to control engine operation. In one example, engines may include a dedicated, standalone pressure sensor positioned in an exhaust passage of the engine, upstream of a catalyst, to measure exhaust pressure. However, some engines may not include an exhaust pressure sensor. Dedicated exhaust pressure sensors may increase engine system costs and engine system control complexity. In another example, the exhaust pressure may be modeled based on alternate engine operating conditions and/or sensor measurements. However, the inventors herein have recognized that these exhaust pressure models may have errors that may cascade into additional models that use the modeled exhaust pressure. Additionally, certain models may be bounded by a window in which exhaust pressure may only be modeled under certain engine operating conditions. As a result, engine control based on exhaust pressure estimates during operation outside of the window may have reduced accuracy.
In one example, the issues described above may be addressed by a method for: estimating an exhaust pressure of exhaust gas flowing through an engine exhaust passage based on a difference between a first output of an oxygen sensor disposed in the exhaust passage and a second output of the oxygen sensor, both the first and second outputs taken after increasing a reference voltage of the oxygen sensor from a lower, first voltage to a higher, second voltage. In this way, an existing engine sensor (e.g., an exhaust oxygen sensor) may be used to more accurately estimate engine exhaust pressure, thereby increasing an accuracy of engine control based on exhaust pressure estimates.
As one example, an exhaust gas sensor (e.g., exhaust oxygen sensor) may be positioned in an exhaust passage of an engine and operated to provide indications of various exhaust gas constituents. Under select conditions, the exhaust gas sensor may be operated as a variable voltage (VVs) oxygen sensor. When operating in the VVs mode, a reference voltage of the exhaust gas sensor is increased from a lower, base voltage (e.g., approximately 450 mv) to a higher, target voltage (e.g., in a range of 900-1100 mV). In some examples, the higher, target voltage may be a voltage at which water molecules are partially or fully dissociated at the oxygen sensor while the base voltage is a voltage at which water molecules are not dissociated at the sensor. The inventors herein have recognized that exhaust gas sensors have a characteristic pressure dependency. Since pressure changes the ability for oxygen to pass through the sensor's diffusion barrier, exhaust pressure changes may be reflected in the sensor's pumping current output, especially while operating in VVs mode. Thus, a method may include generating a first output of the oxygen sensor while the sensor is operating at the higher, second voltage (e.g., target voltage) and then subsequently generating a second output of the oxygen sensor while the sensor is operating at the same second voltage and in a same air-fuel environment (e.g., the exhaust air-fuel ratio is substantially the same during generating both the first and second outputs). The difference between the first and second outputs may then be indicative of a change in exhaust pressure between a time of generating the first output and a time of generating the second output. In some examples, the exhaust pressure at the time of the second output may then be determined. A controller may then adjust engine operation based on the determined change in exhaust pressure and/or exhaust pressure during the time of generating the second output.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.